The development law of silt suction pit morphology under the action of pipeline suction and drainage

Reservoir siltation represents a significant global environmental challenge. Pipeline dredging has emerged as an efficient and adaptable solution for sediment removal, playing an increasingly important role in ecological restoration and capacity recovery of reservoirs. During pipeline dredging, the physical collapse of the suction pit in the siltation layer is a significant source of sediment supply, which directly affects the formation of high-concentration mud and the efficiency and cost of dredging. Most previous studies have focused on the evolution of scour pits under still or low-velocity flow conditions, which fail to capture the development of suction pit morphology during pipeline dredging. This study focus on the development law of suction pit morphology under pipeline suction-discharge conditions, and reveals the mechanism of suction pit’s physical collapse patterns, based on physical model tests of the longitudinal profile and overall morphological changes of the suction pit. Results show that the development of suction pit can be divided into three stages: the initial, stable, and equilibrium. The depth and volume of the suction pit follow an arctangent function over time. At equilibrium, the profile assumes a symmetrical bell-shaped curve with geometrically similar under different operating conditions. Furthermore, the depth and range of the suction pit increase with suction flow rate but decrease as sediment grain size increases. The morphological development equations for the suction pit are derived in light of the sediment and hydrological key factors, and validated against measured data with the average correlation coefficients higher than 0.95, which shows strong agreement. These outcomes provide theoretical support for the design of dredging systems, the optimization of operational schemes, and technical guidance for restoring reservoir capacity.